1. Field of the Invention
The present invention relates generally to a data recording and reproducing system and more particularly to a data recording and reproducing system suited for use in combination with an optical disk system.
2. Description of the Prior Art
As an attempt to implement an apparatus which is capable of recording and reproducing a great amount of information on a single recording surface at an extremely high recording density, active efforts have been made for the development of an optical disk system. The optical disk is generally provided with several millions of tracks in the recording area defined between outer and inner peripheries, wherein each track is divided into a plurality of blocks, which are referred to as sectors and assigned to have inherent addresses, respectively. The recording and reproduction of data are performed on the block or sector basis. In the system which is designed to read the data on a block basis, it is common that the data of each block is recorded together with an ECC (Error Correction Code) so that a data error produced upon reproduction may be corrected by making use of the ECC syndrome.
However, in the hitherto known data recording and reproducing system, such error which has proven to be uncorrectable by an ECC correcting circuit can not be identified as to the location or position within the data block where the uncorrectable error is present. As a consequence, whole data block which contains the error has to be dealt with as the invalid data.
In the optical disk system, information is recorded on a recording film formed on a disk surface in the form of deformation or phase variation of the recording film which is produced through irradiation with a high energy beam generated by a laser. In reproduction, the data or information thus recorded is detected as variations in the intensity of light reflected from the recording surface. In that case, the level of reflected light is easily susceptible to influences, such as variations in the condition of the formed recording film, changes in the irradiation light beam and the like. Such being the circumstance, the probability of error being produced in the data reproduced from the optical disk is at present higher, as compared with the probability of error occurrence in other recording systems, such as a magnetic disk system and the like. Accordingly, it is now an important technical problem to determine how to decrease technically the occurrence of an error in the recorded and reproduced data and, besides, how to correct the produced error to thereby allow the data to be utilized more effectively.